Back to EveryPatent.com
United States Patent |
5,611,199
|
Bray
|
March 18, 1997
|
Two stage electrohydraulic pressure control valve
Abstract
A two-stage electrohydraulic pressure control valve modulatably controls
engagement of a spring applied, pressure released brake when electrical
power directed thereto is suddenly lost. The control valve includes a
shutdown valve mechanism between a pilot stage and a main stage to
controllably reduce the fluid pressure in an accumulator storage chamber
in three distinct stages. The first stage is the immediate blocking of
fluid flow from the storage chamber by a flow control valve when fluid
passing therethrough in one direction exceeds a predetermined flow rate.
The second stage is reducing the fluid pressure in the storage chamber to
a predetermined level by a relief valve when the flow control valve is in
its flow blocking position. The third stage is accomplished by restricting
fluid flow from the storage chamber at a predetermined flow rate through
an orifice so that the main stage modulatably controls the reduction of
fluid pressure in the brake chamber.
Inventors:
|
Bray; Steven C. (Peoria, IL)
|
Assignee:
|
Caterpillar Inc. (Peoria, IL)
|
Appl. No.:
|
572253 |
Filed:
|
December 13, 1995 |
Current U.S. Class: |
60/404; 60/413 |
Intern'l Class: |
F16D 031/02 |
Field of Search: |
60/413,404,405,406
|
References Cited
U.S. Patent Documents
3985063 | Oct., 1976 | Lemon | 60/413.
|
4458791 | Jul., 1984 | Schneider et al. | 60/413.
|
4959957 | Oct., 1990 | Schmale et al. | 60/413.
|
5020322 | Jun., 1991 | Schwarz | 60/404.
|
5355676 | Oct., 1994 | Inokuchi | 60/413.
|
Foreign Patent Documents |
1234388 | Jun., 1971 | GB | 60/413.
|
Primary Examiner: Ryznic; John E.
Attorney, Agent or Firm: Grant; John W.
Claims
I claim:
1. A two stage electrohydraulic pressure control valve comprising:
a force controlled main stage having first and second ends and an output
port connected to the first end;
an energy storage device having a storage chamber connected to the second
end of the main stage; and
a shutdown valve mechanism connected to the storage chamber and having flow
control means for blocking fluid flow from the storage chamber when fluid
passing through the flow control means exceeds a predetermined flow rate,
and flow restricting means for restricting fluid flow from the storage
chamber; and
a solenoid controlled pilot stage connected to the shutdown valve
mechanism.
2. The pressure control valve of claim 1 wherein the shutdown mechanism
includes pressure relieving means for reducing fluid pressure in the
storage chamber to a predetermined level when the fluid control means is
in the flow blocking condition.
3. The pressure control valve of claim 2 wherein the flow control means
includes a flow control valve movable between open and closed positions
and being resiliently biased to the open position, the flow control valve
having an orifice sized to generate a pressure differential thereacross
sufficient to move the flow control valve to the closed position when
fluid passing therethrough exceeds the predetermined flow rate.
4. The pressure control valve of claim 3 wherein the pressure relieving
means includes a pressure relief valve disposed in parallel with the flow
control valve and has closed and open positions, and which is resiliently
biased to the closed position and is movable to the open position when
pressure in the storage chamber exceeds the predetermined level and the
flow control valve is in the closed position.
5. The pressure control valve of claim 4 wherein the flow restricting means
includes a modulating orifice disposed in parallel with the pressure
relief valve.
6. The pressure control valve of claim 5 wherein the flow control valve,
pressure relief valve, and modulating orifice are integrated within a
common valve.
7. The pressure control valve of claim 6 where the common valve includes a
housing having a bore therein, a spool slidably disposed in the bore and
movable between a first position establishing the open position of the
flow control valve and the blocking position of the relief valve, a second
position establishing the closed position of the flow control valve and
the open position of the pressure relief valve, and a third position
establishing the modulating orifice and the closed positions of the flow
control valve and the relief valve, and a spring biasing the spool toward
the first position.
8. The pressure control valve of claim 7 wherein the spool defines a first
chamber connected to the pilot stage and a second chamber connected to the
storage chamber and the second end of the main stage.
9. The pressure control valve of claim 8 wherein the spool includes an
axially extending passage opening into the first chamber and a radial
passage communicating the second chamber with the passage at the first and
second positions of the spool.
10. The pressure control valve of claim 9 including a predetermined annular
clearance defined between the spool and the bore and the radial passage
communicates the annular clearance with the axially extending passage at
the third position of the spool.
11. The pressure control valve of claim 10 wherein the pilot stage is
hydraulically connected to the shutdown valve mechanism and is biased to
an open position when no electrical power is transmitted thereto.
12. The pressure control valve of claim 10 wherein the pilot stage is
mechanically connected to the shutdown valve mechanism, the shutdown valve
mechanism having an inlet port and an outlet port.
Description
TECHNICAL FIELD
This invention relates to a two stage electrohydraulic pressure control
valve and, more particularly, to one suitable for controlling a spring
applied pressure released brake in which the brake is controllably engaged
when the electrical power to the control valve is lost.
BACKGROUND ART
Two stage electrohydraulic pressure control valves are increasingly being
used in diverse applications for controlling such things as hydraulic
control valves, brakes, clutches, and so forth. In many cases, those
valves are controlled by a microprocessor and the control system,
including such valves, can be made extremely versatile simply by changing
the microprocessor program. One example is where a two stage
electrohydraulic pressure control valve is used to controllably release
and engage a spring applied pressure released brake. Such brakes are
normally maintained in a disengaged position by a high electrical signal
directed to the solenoid actuated pilot stage and is engaged by decreasing
the electrical power to the solenoid. Under normal operating conditions,
the electronics can be programmed to control the rate of decrease in the
electrical power and thus modulate the engagement of the brake under
controlled conditions.
However, one of the problems encountered occurs when an electrical
malfunction occurs and the control valve is uncontrollably moved to a
brake engaged position. When this happens, the brakes could be applied
very abruptly without any warning to the operator.
Thus, what is needed is a two stage electrohydraulic pressure control valve
that includes a mechanism for modulatably controlling the engagement of a
spring applied pressure released brake when the electrical power to the
solenoid is suddenly lost.
The present invention is directed to overcoming one or more of the problems
as set forth above.
DISCLOSURE OF THE INVENTION
In one aspect of the present invention, a two stage electrohydraulic
pressure control valve includes a force controlled main stage having first
and second ends and an output port connected to the first end, an energy
storage device having a storage chamber connected to the second end of the
main stage, and a shutdown valve mechanism connected to the storage
chamber. The shutdown valve mechanism has a flow control means for
blocking fluid flow from the storage chamber when fluid passing through
the fluid control means exceeds a predetermined flow rate, and flow
restricting means for restricting fluid flow from the storage chamber. A
solenoid controlled pilot stage is connected to the shutdown valve
mechanism.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1, 2 and 4 are diagrammatic schematic illustrations of alternate
embodiments of the present invention;
FIG. 3 is a cross sectional view taken along line 3--3 of FIG. 2; and
FIG. 5 is a pressure/time curve illustrating features of the present
invention.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring to FIG. 1, a two stage electrohydraulic pressure control valve 10
receives fluid from a pump 11 and directs a control pressure to a fluid
chamber 12 of a spring applied pressure released brake 13. The brake 13
has a spring 14 for applying or engaging the brake.
The control valve 10 includes a solenoid controlled pilot stage 16, a force
controlled main stage 17, an energy storage means 18 for allowing
instantaneous independent movement of the main stage relative to the pilot
stage and a shutdown mechanism 19. The pilot stage valve 16 has an input
port 20 connected to the pump 11 through a fixed supply orifice 21, a
drain port 22 connected to a tank 23, and a regulated pressure passage 24
continuously communicating with an end 26 of the pilot stage.
The main stage 17 is connected to the pump 11 through an input port 28 and
to the fluid chamber 12 through an outlet port 29 which continuously
communicates with an end 31 of the main stage. The pilot stage 16 provides
a regulated pressure at lower flows for the larger main stage that handles
the main control flow from the pump to the brake.
The energy storage means 18 includes an accumulator 32 having a piston 33,
a fluid storage chamber 34 defined at one side of the piston and connected
to another end 36 of the main stage through a passage 37, and a spring 38
disposed at the other end of the piston. While the accumulator 32 is shown
separated from the main stage, they can advantageously be positioned
within a common bore and share a common fluid chamber connected to the
passage 37.
The shutdown valve mechanism 19 in this embodiment is disposed between the
passages 24 and 37 and has a flow control means 39 for blocking fluid flow
from the storage chamber 34 to the pilot stage 16 when fluid flow passing
therethrough from the passage 37 to the passage 24 exceeds a predetermined
flow rate, a pressure relieving means 41 for reducing the fluid pressure
in the storage chamber 34 when the flow control means is in a flow
blocking mode, and a flow restricting means 42 for restricting fluid flow
from the storage chamber to the passage 24.
The flow control means 39 includes a flow control valve 43 disposed between
the passages 24 and 37 which continuously communicate with opposite ends
44,46 respectively. The flow control valve is movable between open and
closed positions and is biased to the open position shown by a spring 47.
Fluid pressure in the passage 24 exerts a spring aiding force against the
flow control valve while fluid pressure in the passage 37 exerts a spring
opposing force against the flow control valve. A trigger orifice 48 is
serially disposed between the passages 24 and 37.
The pressure relieving means 41 includes a pressure relief valve 51
disposed between and connected to the passages 24 and 37 in parallel to
the flow control valve 46. The relief valve is biased to a closed position
shown by a spring 52 disposed at an end 53. The passage 24 continuously
communicates with the end 53 so that a spring aiding force is applied to
the relief valve. The passage 37 continuously communicates with an end 54
so that a spring opposing force is exerted on the relief valve.
The means 42 includes a modulating orifice 56 disposed between the passages
24 and 37 and in parallel with the flow control valve and the relief
valve.
An alternate embodiment of a pressure control valve 10 of the present
invention is disclosed in FIGS. 2 and 3. It is noted that the same
reference numerals of the first embodiment are used to designate similarly
constructed counterpart elements of this embodiment. In this embodiment,
however, the functional aspects of the flow control, pressure relieving
and flow restricting means 39,41,42 are all incorporated within a single
shutdown valve mechanism 19. The valve mechanism includes a spool 58
slidably disposed within a bore 59 of a cylindrical insert 61 suitably
fixed within a body 62. A flange 63 is connected to the spool 58 and
disposed within a chamber 64. The spool includes a longitudinally
extending passage 66 opening into the chamber 64 and three
circumferentially spaced radial passage 67 communicating with the passage
66. A spring 68 is disposed between the insert 61 and a retainer 69
suitably secured to the spool 58 for resiliently biasing the spool to the
position shown as determined by engagement between the flange 63 and the
insert 61. As more clearly shown in FIG. 3, a pair of parallel slots 71 in
the insert communicate the bore 59 with a chamber 72 in the housing 62.
The passage 24 communicates with the passage 64 through a port 73 while
the passage 37 communicates with the port 72 through a port 74. The
functions of the springs 47,52 of FIG. 1 are embodied within the single
spring 68 of this embodiment. The diameter of the spool 58 is slightly
smaller than the diameter of the bore 59 to provide a diametral clearance
76 (exaggerated for illustration in FIG. 3). The interaction between the
passages 67 and the clearance 76 serve to establish the modulating orifice
56 when the spool is moved leftward and the passages 67 enter the bore 59.
The passages 67 provide the function of the orifice 48 of the flow control
valve 43 in FIG. 1. Finally, the coaction between the passages 67 and the
slots 71 upon extreme leftward movement of the spool 58 against the bias
of the spring 68 serve as the relief valve 51 of the FIG. 1 embodiment.
Another embodiment of a pressure control valve 10 of the present invention
is disclosed in FIG. 4. It is noted that the same reference numerals of
the first and second embodiment are used to designate similarly
constructed counterpart elements of this embodiment. In this embodiment,
however, the pilot stage 16 is integrated into the shutdown valve
mechanism 19 as represented schematically by the reference numeral 77. The
integrated valve mechanism 77 includes a spool 78 for controlling fluid
flow between an input port 79 and the passage 37 and between the passage
37 and an outlet port 80. A shutdown spring 81 is maintained in a
preloaded condition and constrained so it does not affect normal opening
of the pilot stage. The valve spool 78 is movable between four operating
positions represented by the letters A,B,C and D. The "A" position
provides the function of the pilot stage, the "B" position provides the
function of the flow control valve, the "C" position provides the function
of the modulating orifice, and the "D" position provides the function of
the shutdown relief valve.
FIG. 5 is a graph illustrating a pressure decay versus time when the
electrical power to the pilot stage is lost. Curve "A" depicts the rate of
pressure decay when the relief valve is open, curve "B" depicts the rate
of pressure decay when the accumulator chamber is being vented through the
modulation orifice and curve "C" depicts the rate of pressure decay when
the flow control valve reopens.
Industrial Applicability
The pressure control valve of FIG. 1 is shown in its brake disengaged
position for convenience in describing the operation thereof. More
specifically, the pilot stage 16 is shown in an energized position
established by directing electrical power thereto to regulate the pressure
in the passages 24 and 37 such that the actuating chamber 34 is filled
with pressurized fluid. The fluid pressure in the passage 37 also urges
the main stage 17 to the position shown to communicate fluid from the pump
to the brake chamber 12 such that the spring 14 is compressed and the
brake disengaged.
Should electrical power to the pilot stage 16 be lost, the pilotstage
immediately opens communicating the passage 24 to the tank 23. This
removes the spring adiding force exerted on the flow control valve 46 and
the relief valve 51 and creates a flow path from the chamber 32 to the
tank through the orifice 48. The initial rush of fluid flowing through the
orifice 48 creates a pressure drop there across and a spring opposing
force is exerted on the flow control valve sufficient to move it to its
closed portion. When the flow control valve closes, a spring opposing
force is then exerted on the relief valve 51 sufficient to open it thereby
quickly dropping the pressure in the passage 37 to a predetermined level
represented by the junction of lines "A" and "B" on FIG. 5 and then
closes. As the pressure in the passage 37 decays, the main stage 17 stage
starts to move to a position initiating venting of the brake chamber 12.
The predetermined pressure level in these embodiments is selected so that
the spring 14 initiates engagement of the brake slightly before the
predetermined pressure level is reached. The closing of the relief valve
forces the remaining fluid in the actuating chamber 32 to pass through the
shutdown orifice 56 which slowly drains the fluid to decrease the pressure
in the accumulator chamber 34 at a rate depicted by the line "B" on FIG.
5. During this phase, the brakes are modulatably engaged. When the
pressure decays to a level depicated by the junction of lines "B" and "C",
the flow control valve reopens and full force of the spring is utilized
for applying the brake.
During normal operation, the electrical power to the pilot stage is
controllably reduced at a rate that will not cause the flow control valve
to move to its closed position.
Engagement of the brake of the FIG. 2 embodiment is substantially the same
as described above with the exception that the fluid control valve, relief
valve and shut down modulating orifice functions are provided by the same
spool 5. More specifically, when the pressure in the chamber 64 is
suddenly reduced due to a power loss to the pilot stage, the sudden rush
of fluid through the passages 67 from the passage 37 and accumulator
chamber 34 create a pressure drop there across sufficient to move the
spool leftward. When the passages 67 enter the bore 59, communication
between the chamber 72 and the passage 66 is substantially blocked such
that the pressure in the chamber 72 thereby acts to quickly move the spool
to the pressure reliving position established by at least one of the
passages 67 opening into one of the slots 71. When the pressure in the
chamber 72 decays to the predetermined level, as described above, the
valve spool 58 moves rightward causing the passages 67 to re-enter the
bore 59 to establish the shutdown modulating orifice 61. As the pressure
in the chamber 72 and the accumulator chamber 34 is reduced by the
shutdown orifice 61, the spool 67 gradually moves rightward until the
passages 67 exit the bore to again establish the open position of the flow
control valve, thereby draining off the remaining pressure in the
accumulator chamber 34.
The pressure control valve of the embodiment of FIG. 4 functions similarly
to that described above with the exception that the passage 37 is
connected to the outlet port 80 at the "B", "C" and "D" positions as
opposed to passing through the pilot stage as described above. Moreover,
directing electrical power to the solenoid causes the spool to move
rightward to the position "A" such that the pilot stage functions as a
proportional valve to maintain the pressure in the passage 37 at a level
proportional to the strength of the power to the solenoid.
In view of the above, it is readily apparent that the structure of the
present invention provides a two-stage electrohydraulic pressure control
valve 10 that modulatably controls engagement of a spring applied,
pressure released brake 13 when electrical power directed thereto is
suddenly lost. This is accomplished by incorporating a shutdown valve
mechanism 19 between a pilot stage 16 and a main stage 17 to controllably
reduce the fluid pressure in an accumulator storage chamber 34 in three
distinct stages. The first stage is the immediate blocking of fluid flow
from the storage chamber by a flow control valve 46 when fluid passing
therethrough in one direction exceeds a predetermined flow rate. The
second stage is reducing the fluid pressure in the storage chamber to a
predetermined level by a relief valve 51 when the flow control valve is in
its flow blocking position. The third stage is accomplished by restricting
fluid flow from the storage chamber at a predetermined flow rate so that
the main stage modulatably controls the reduction of fluid pressure in the
brake chamber 12.
Other aspects, objects, and advantages of this invention can be obtained
from a study of the drawing, the disclosure and the appended claims.
Top